1. Field of the Invention
This invention generally relates to an electronic device, a method for controlling the same, and an optical semiconductor device. More particularly, the present invention relates to an electronic device equipped with a DC/DC converter, a method for controlling such an electronic device, and an optical semiconductor module.
2. Description of the Related Art
Electronic devices having electronic circuits are used in various fields. Electronic circuits built in the electronic devices are supplied as semiconductor devices such as integrated circuits. The electronic devices are supplied with a power supply voltage that falls within a defined range prescribed as a recommended operating condition. The recommended operating condition is an operating condition guaranteed by the supplier of the electronic circuits. The electronic circuits incorporated into the electronic devices are supplied with the power supply voltages within the range of the recommended operating condition.
A conventional electronic device will now be described. FIG. 1 is a block diagram of an electronic device 60a equipped with an electronic circuit 50. The electronic device 60a may include multiple electronic circuits 50. Here, it is assumed that the electronic device 60a has one electronic circuit 50. The recommended operating condition for a power supply input to the electronic circuit 50 is assumed as Vc(1±α) where Vc is the center value of the recommended operating condition for the voltage of the power supply input to the electronic circuit 50, while the lower limit Vmin of the recommended operating condition is equal to Vc(1−α) and the upper limit Vmax thereof is equal to Vc(1+α). When the electronic circuit 50 is supplied with Vc, Vmin or Vmax, the electronic circuit 50 consumes current Ic, Imin=Ic(1−β) or Imax=Ic(1+β), respectively. The power supply inputs of the electronic circuit 50 are directly connected to an external power supply outside of the electronic device 60a and ground. Generally, the power supply voltage Vc is applied to the electronic circuit 50.
FIG. 2 is a block diagram for explaining the voltage of an external power supply generally used. As shown in the left-side portion of FIG. 2, the recommended operating condition for the power supply input voltage of the electronic circuit 50 ranges from Vmin to Vmax at the center of V1. When a variation (assumed as Vs) in the power supply voltage is considered, the usable range as the power supply input to the electronic circuit 50 is V2 that ranges from Vmin+Vs to Vmax−Vs. When it is further considered that there is a voltage drop Vd that develops in a connector and a substrate line in the circuit from the external power supply to the electronic circuit 50, the voltage supplied from the external power supply falls within a range V3 of Vmin+Vs+Vd to Vmax−Vs+Vd. When variations in the power supply voltage are considered as mentioned above, the voltage of the external power supply is used in the vicinity of Vc. If the circuit is greatly affected by the voltage drop, the voltage of the external power supply is used in the vicinity of Vc+Vd.
When it is assumed that Vc is supplied from the external power supply for the electronic device 60a without considering the influence of the voltage drop, the voltage of the power supply input to the electronic circuit 50 is Vc, and power P of the electronic device 60a (that is, the electronic circuit 50) is expressed as follows:P=Vc×Ic  (1)where Ic is current consumed in the electronic circuit 50 as has been defined previously.
In the electronic device 60a, Vmax is the allowable maximum voltage of the external power supply as long as the recommended operating condition of the power supply input to the electronic circuit 50 is satisfied. When Vmax is supplied from the external power supply, the maximum power Pmax of the electronic circuit 50 is expressed as follows:Pmax=Vc(1+α)×Ic(1+β)  (2)As described above, when the voltage of the external power supply varies, the power of the electronic device 60a is changed.
Japanese Patent Application Publication No. 2005-245152 discloses a DC/DC converter.
The electronic devices are required to reduce power consumed in the internal electronic circuits.